1. Field of the Invention
This invention relates in general to magnetic transducers for reading information signals from a magnetic medium and, in particular, to an improved magnetoresistive read transducer.
2. Description of the Prior Art
The prior art discloses a magnetic transducer referred to as a magnetoresistive (MR) sensor or head which has been shown to be capable of reading data from a magnetic surface at great linear densities. An MR sensor detects magnetic field signals through the resistance changes of a read element made from a magnetoresistive material as a function of the amount and direction of magnetic flux being sensed by the element.
In the past, principal problems with the MR sensors of unstable operating characteristics have limited their use. One of the sources of unstable operating characteristics has been the conductive lead structures by which resistance variations of the MR film have been sensed. The conductive lead structures have comprised the well-known low resistivity materials which are good electrical conductors. For example U.S. Pat. No. 4,622,613 to Nomura et al describes an MR sensor in which the conductive lead structures are formed of copper, gold, and silver. U.S. Pat. No. 4,663,684 to Kamo et al describes an MR senor in which the conductive lead structures are formed of gold or aluminum. U.S. Pat. No. 4,503,394 discloses an MR sensor in which the conductive lead structures are formed of a two layer assembly in which the first layer is made from a material selected from the group consisting of Cr, Mo, and Ti and the second layer is made from a material selected from the group consisting of Al, Au, Pt and Pd.
The problems that have arisen in MR sensors using the prior art conductive lead structures include high stress, poor adhesion and etchant penetration in subsequent sensor processing which leads to damage and/or degradation to the MR sensors. In addition, problems of interdiffusion and electromigration have caused changes in the electrical characteristics of the sensor during the service life of the MR sensors. A further problem relates to physical changes in the MR sensor due to extrusion and scratching damage at the part of the MR sensor which extends to the air bearing surface.
The prior art has not shown an MR sensor having conductive lead structures which are stable not only in subsequent processing of the MR sensor during manufacture but also are stable over the anticipated useful life of the MR sensor.